Method for producing bis(trifluoromethyl)imido salts

ABSTRACT

The present invention relates to a novel process for the preparation of bis(trifluoromethyl)imido salts of the general formula (I):  
     [M a+ ] − [N(CF 3 ) 2 ] a   (I)

[0001] The present invention relates to novel processes for the preparation of bis(trifluoromethyl)imido salts of the general formula (I):

[M^(a+)]⁻[N(CF₃)₂]_(a)  (I)

[0002] The chemistry of the bis(trifluoromethyl)imido anion is generally based on the chemical reaction of perfluoro(2-azapropene), CF₃N═CF₂, as starting material (H. G. Ang and Y. C. Syn, Advances in Inorganic Chemistry and Radiochemistry, Vol. 16 (1974), pp. 1-64; A. Haas, Gmelin Handbook of Inorganic Chemistry, 8^(th) Edition, Springer Verlag: Berlin, Heidelberg, New York (1991), Part 9, pp. 125-153; A. Haas, Gmelin Handbook of Inorganic Chemistry, 8^(th) Edition, Springer Verlag: Berlin, Heidelberg, New York (1991), Suppl. Vol. 6, pp. 196-214). This compound can be prepared by fluorination of CCl₃N═CCl₂ using NaF in sulfolane at 105° C. in a yield of 78% (E. Klauke, H. Holtschmidt, K. Findeisen, Farbenfabriken Bayer AG, DE-A1-2101107 (1971/1972)) or by photolysis of CF₃N—(CF₂CFCl₂)Cl (G. Sawar, R. L. Kirchmeier and J. M. Shreeve, Inorg. Chem. 28 (1989, pp. 2187-2189)) in gas at room temperature (boiling point −33° C.), with special industrial apparatuses being necessary for the said compound.

[0003] Di[bis(trifluoromethyl)imido]mercury, Hg[N(CF₃)₂]₂, which is very reactive, was synthesised for the first time by Young and his co-workers (J. A. Young, S. N. Tsoukalas and R. D. Dresdner, J. Am. Chem. Soc. 80 (1958), pp. 3604-3606). This compound is a good reagent for the introduction of N(CF₃)₂ groups into organic molecules (H. G. Ang and Y. C. Syn, see above; A. Haas, Gmelin Handbook of Inorganic Chemistry, 8^(th) edition, Springer Verlag: Berlin, Heidelberg, New York (1981), Part 9, pp. 45-46), but is not a very stable compound since it is extremely sensitive to moisture. The synthesis of Hg[N(CF₃)₂]₂ is difficult, time-consuming and requires special industrial apparatuses and expensive starting materials.

[0004] Caesium bis(trifluoromethyl)imide, [Cs]⁺[N(CF₃)₂]⁻, is a further option for the synthesis of bis(trifluoromethyl)amino compounds. This salt is prepared by simply passing perfluoro(2-azapropene) into a solution of caesium fluoride in dry acetonitrile (A. F. Gontar, E. G. Bykovskaja and I. L. Knunyants, IZV. Akad. Nauk SSSR, Otd. Khim, Nauk (1975), pp. 2279-2282). The disadvantage of this method consists in the formation of a dimeric product through the reaction of the starting material perfluoro(2-azapropene) with the caesium salt that has already formed. This reaction is unavoidable and results in the formation of complex product mixtures.

[0005] However, N(CF₃)₂ anions are readily accessible through the reaction of some metal fluorides with N,N-bis(trifluoromethyl)perfluoroalkanesulfonamides or -acylamides [“N(CF₃)₂ anion preparation, and its use”, EP 99 101 982]. This process enables the generation of Na, K, Rb, Cs, Ag, Cu(II) and Hg(II) salts with N(CF₃)₂ anions. However, the analogous reaction of N,N-bis(trifluoromethyl)perfluoroalkanesulfonamides or -acylamides with other metal fluorides (for example ZnF₂ and CdF₂) progresses only very slowly due to the poor solubility of these fluorides in organic solvents.

[0006] The object of the present invention was therefore to provide an improved process for the preparation of bis(trifluoromethyl)imido salts.

[0007] The object according to the invention is achieved by a process for the preparation of bis(trifluoromethyl)imido salts of the general formula (I)

[M^(a+)][(N(CF₃)₂)⁻]₈   (I)

[0008] in which

[0009] M^(a+) is a monovalent or divalent cation, and a=1 or 2,

[0010] characterised in that at least one trifluoromethanesulfonate of the general formula (II)

[M^(a+)][(OSO₂CF₃)⁻]_(a)   (II)

[0011] in which

[0012] M^(a+) is a monovalent or divalent cation, and a=1 or 2,

[0013] is reacted with bis(trifluoromethyl)imidorubidium in solution, and the resultant bis(trifluoromethyl)imido salt of the general formula (I) is, if desired, purified and/or isolated by conventional methods.

[0014] Preference is given to processes according to the invention in which M^(a+) is a sodium, potassium, caesium, copper or silver cation, and a=1.

[0015] Particular preference is given to processes according to the invention in which M^(a+) is a mercury, copper, zinc or cadmium cation, and a=2.

[0016] Particular preference is also given to processes according to the invention in which a=1 and M^(a+) is a cation of the general formula (III)

[([R_(b) ¹R_(c) ²R_(d) ³R_(e) ⁴]A_(x))_(y)Kt]⁺   (III)

[0017] in which

[0018] Kt═N, P, As, Sb, S or Se,

[0019] A═N, P, P(O), O, S, S(O), SO₂, As, As(O), Sb or Sb(O),

[0020] R¹, R², R³ and R⁴ are identical or different and are

[0021] H, halogen, substituted and/or unsubstituted alkyl C_(n)H_(2n+1), substituted and/or unsubstituted C₁₋₁₈-alkenyl having one or more double bonds, substituted and/or unsubstituted C₁₋₁₈-alkynyl having one or more triple bonds, substituted and/or unsubstituted cycloalkyl C_(m)H_(2m−1), monosubstituted, polysubstituted and/or unsubstituted phenyl, substituted and/or unsubstituted heteroaryl;

[0022] where

[0023] n=1-18,

[0024] m=3-7,

[0025] x=0 or 1,

[0026] y=1-4,y=1 for x=0,

[0027] where

[0028] b, c, d and e are each =0 or 1, where b+c+d+e≠0,

[0029] A may be included in various positions in R¹, R², R³ and/or R⁴,

[0030] Kt may be included in a cyclic or heterocyclic ring,

[0031] the groups bonded to Kt may be identical or different.

[0032] The processes according to the invention also enable the preparation of novel bis(trifluoromethyl)imido salts which are difficult to access, such as, for example, cadmium, zinc or copper(I) N(CF₃)₂ salts. Novel salts therefore represent a further subject-matter of the present invention.

[0033] The salts prepared in accordance with the invention can be used alone or in mixtures with other salts as conductive salts or additives in electrolytes. Besides the salt or salt mixtures, the electrolytes also comprise solvents or solvent mixtures.

[0034] These electrolytes are employed in electrochemical cells (such as, for example, primary and secondary batteries). They are preferably employed in capacitors and supercapacitors.

[0035] The starting materials bis(trifluoromethyl)imidorubidium and the trifluoromethanesulfonate salts are both readily soluble in a number of organic solvents. In addition, metal triflates are commercially available from a number of companies.

[0036] The reaction of Rb[N(CF₃)₂] and metal triflates at room temperature or below takes place rapidly, for example in accordance with the following general reaction scheme:

xRb[N(cf₃)₂]+M(OSO₂CF₃)_(x)→M[N(CF₃)₂]_(x)+xRb(OSO₂CF₃)

[0037] In the process according to the invention, the conversion to a bis(trifluoromethyl)imido salt of the general formula (I) is preferably carried out at a temperature of from −60 to +60° C., particularly preferably from −50 to +50° C., very particularly preferably at from −45 to +30° C.

[0038] Preferred solvents for the conversion to a bis(trifluoromethyl)imido salt of the general formula (I) are organic solvents, particularly preferably polar organic solvents.

[0039] Very particularly preferred solvents for the conversion to a bis(trifluoromethyl)imido salt of the general formula (I) are the solvents acetonitrile, benzonitrile, dimethoxyethane and/or propionitrile or a mixture of acetonitrile, benzonitrile, dimethoxyethane and/or propionitrile.

[0040] Preferred solvents according to the invention comprise ≦0.1% by weight of water, preferably ≦0.01% by weight of water, particularly preferably ≦0.005% by weight of water.

[0041] In the preferred processes according to the invention, the trifluoromethanesulfonate salt of the general formula (II) or the bis(trifluoromethyl)imidorubidium is employed in a molar excess of ≦3% or particularly preferably in equimolar amounts.

[0042] The rubidium triflate formed by the process according to the invention has limited solubility in organic solvents and can be separated off from the reaction mixture as a solid at low temperatures.

[0043] Preferred processes according to the invention are therefore those in which the bis(trifluoromethyl)imido salt of the general formula (I) is purified by filtration at a temperature of from −90 to +30° C., particularly preferably at from −70 to +20° C., after removal of the solvent.

[0044] Further purification of a bis(trifluoromethyl)imido salt of the general formula (I) is possible by extraction with dichloromethane and/or hexane and/or diethyl ether. Extraction with dichloromethane is a preferred variant of the present invention.

[0045] The invention is explained below with reference to examples. These examples serve merely to explain the invention and do not restrict the general inventive idea.

EXAMPLES Example 1 Synthesis of Bis(trifluoromethyl)imidosilver Salt

[0046] A solution of Rb[N(CF₃)₂] salt prepared from 0.083 g (0.79 mmol) of rubidium fluoride and 0.227 g (0.79 mmol) of CF₃SO₂N(CF₃)₂ in 3.2 ml of dry acetonitrile was added to a solution, cooled to −20° C., of 0.205 g (0.79 mmol) of AgOSO₂CF₃ in 1.8 ml of dry acetonitrile with stirring. The mixture was stirred at −20° C. for one hour. A white sediment formed in the process. The solvent acetonitrile was removed by suction filtration at −20° C., and 4 ml of dry dichloromethane were added to the residue. After the mixture had been stirred at −20° C. for ten minutes, the solution was separated from the residue, and the solvent was removed by suction filtration at −20° C. 0.149 g of Ag[N(CF₃)₂]·CH₃CN was obtained as a white crystalline substance, as demonstrated by analysis. The yield was 62.3%.

[0047] Analysis (amperometric titration):

[0048] Yield: 35.76% (Ag⁺);

[0049] Theoretical value for Ag[N(CF₃)₂]·CH₃CN: 35.85% (Ag⁺);

[0050]¹⁹F NMR spectrum (solvent CD₂Cl₂, reference substance CCl₃F),

[0051] ppm: −44.56 s (CF₃)

[0052]¹H NMR spectrum (solvent CD₂Cl₂, reference substance TMS),

[0053] ppm: 2.08 s (CH₃CN)

[0054]¹⁰⁹Ag NMR spectrum (solvent CD₂Cl₂, reference point: chemical shift of 1M AgNO₃ in D₂O set to 0),

[0055] ppm: 316.23 s, Ag

Example 2 Synthesis of Bis(trifluoromethyl)imidocopper(I) Salt

[0056] A solution of Rb[N(CF₃)₂] salt prepared from 0.080 g (0.766 mmol) of rubidium fluoride and 0.218 g (0.766 mmol) of CF₃SO₂N(CF₃)₂ in 3.2 ml of dry acetonitrile was added at room temperature to a solution of 0.194 g (0.766 mmol) of CuOSO₂CF₃·CH₃CN in 1.8 ml of dry acetonitrile with stirring. The mixture was stirred for one hour. A white sediment formed in the process. The solvent acetonitrile was removed by suction filtration at room temperature, and 4 ml of dry dichloromethane were added to the residue. After the mixture had been stirred at room temperature for ten minutes, the solution was separated from the residue, and the solvent was removed by suction filtration at room temperature. 0.150 g of Cu[N(CF₃)₂]·CH₃CN was obtained as a white crystalline substance, as demonstrated by analysis. The yield was 76.5%.

[0057]¹⁹F NMR spectrum (solvent CD₂Cl₂, reference substance CCl₃F),

[0058] ppm: −44.79 s (CF₃)

[0059]¹H-NMR spectrum (solvent CD₂Cl₂, reference substance TMS),

[0060] ppm: 2.03 s, CH₃CN

Example 3 Synthesis of Bis(trifluoromethyl)imidozinc Salt

[0061] A solution of Rb[N(CF₃)₂] salt prepared from 0.080 g (0.766 mmol) of rubidium fluoride and 0.218 g (0.766 mmol) of CF₃SO₂N(CF₃)₂ in 3.2 ml of dry propionitrile was added at −45° C. to a solution of 0.155 g (0.383 mmol) of Zn(OSO₂CF₃)₂·CH₃CN in 1.8 ml of dry propionitrile with stirring. The mixture was stirred for one hour at −45° C. A white sediment formed in the process. The mixture was then cooled to −78° C. and left at this temperature without stirring for two hours. The solvent was removed by suction filtration, a small amount of CD₃CN (about 30%) was added, and the mixture was characterised by ¹⁹F NMR spectroscopy at −45° C. The signal at −44.83 ppm is assigned to Zn[N(CF₃)₂ 1 ₂, which is coordinated with the solvent. In order to isolate the salt, the solvent was removed by suction filtration at −30° C., and the white solid which remained was, after dissolution in dry CD₂Cl₂, employed for NMR spectroscopy. The NMR spectrum showed the presence of the propionitrile in the crystal structure of the Zn[N(CF₃)₂]₂·C₂H₅CN salt. This salt has only low stability as analysis substance at room temperature.

[0062]¹⁹F NMR spectrum at −40° C. (solvent CD₂Cl₂, reference substance CCl₃F),

[0063] ppm: −45.97 s (CF₃, the position of the signal is concentration-dependent)

[0064]¹H NMR spectrum at −40° C. (solvent CD₂Cl₂, reference substance TMS),

[0065] ppm: 1.08 t (CH₃); 2.25 q (CH₂), C₂H₅CN

Example 4 Synthesis of Bis(trifluoromethyl)imidocadmium Salt

[0066] A solution of Rb[N(CF₃)₂] salt prepared from 0.080 g (0.766 mmol) of rubidium fluoride and 0.218 g (0.766 mmol) of CF₃SO₂N(CF₃)₂ in 3.2 ml of dry propionitrile was added at −45° C. to a solution of 0.188 g (0.383 mmol) of Cd(OSO₂CF₃)₂·2CH₃CN in 1.8 ml of dry propionitrile with stirring. The mixture was stirred for one hour at −45° C. A white sediment formed in the process. the mixture was then cooled to −78° C. and left at this temperature without stirring for two hours. The solvent was removed by suction filtration, a small amount of CD₃CN (about 30% by volume) was added, and the mixture was characterised by ¹⁹F NMR spectroscopy at −40° C. The signal at −42.53 ppm is assigned to Cd[N(CF₃)₂]₂, which is coordinated with the solvent. At room temperature, the signal of the N(CF₃)₂ group in the ¹⁹F NMR spectrum shifts to −45.39 ppm. The Cd[N(CF₃)₂]₂·nC₂H₅CN salt has only low stability as analysis substance at room temperature.

Example 5 Electrochemical Stability of [N(C₂H₅)₄][N(CF₃)₂]

[0067] In each case, a number of cyclic voltammograms were recorded successively in a measurement cell with platinum electrode, lithium counterelectrode and lithium reference electrode. To this end, the potential was firstly increased, starting from the rest potential, to 6 V against Li/Li⁺ at a rate of 20 mV/s and then returned to the rest potential. The electrolyte used was a solution of [N(C₂H₅)₄][N(CF₃)₂] in propylene carbonate.

[0068] The characteristic curve shape shown in FIG. 1 is evident, with an oxidation potential E_(ox) of greater than 5 V against Li/Li⁺.

Example 6 Ionic Conductivity of an Electrolyte Based on [N(C₂H₅)₄][N(CF₃)₂]

[0069] With the aid of a 4-pole Knick conductometer, the conductivities of [N(C₂H₅)₄][N(CF₃)₂] in acetonitrile were measured as a function of temperature and concentration of the conductive salt. In parallel, [N(C₂H₅)₄][BF₄] was measured in acetonitrile. This system represents the current state of the art with respect to “supercapacitor” electrolytes and thus serves as reference. FIGS. 2 and 3 show the results obtained. They confirm that the novel system based on [N(C₂H₅)₄][N(CF₃)₂] has significantly improved conductivities. 

1. Process for the preparation of bis(trifluoromethyl)imido salts of the general formula (I) M^(a+)(N(CF₃)₂)⁻]_(a)  (I) in which M^(a+) is a monovalent or divalent cation, and a=1 or 2, characterised in that at least one trifluoromethanesulfonate of the general formula (II) [M^(a+)][(OSO₂CF₃)⁻]_(a)  (II) in which M^(a+) is a monovalent or divalent cation, and a=1 or 2, is reacted with bis(trifluoromethyl)imidorubidium in solution, and the resultant bis(trifluoromethyl)imido salt of the general formula (I) is, if desired, purified and/or isolated by conventional methods.
 2. Process according to claim 1, characterised in that M^(a+) is a sodium, potassium, caesium, copper or silver cation, and a=1.
 3. Process according to claim 1, characterised in that M^(a+) is a mercury, copper, zinc or cadmium cation, and a=2.
 4. Process according to claim 1, characterised in that a=1 and M^(a+) is a cation of the general formula (III) [([R_(b) ¹R_(c) ²R_(d) ³R_(e) ⁴]A_(x))_(y)Kt]⁺  (III) in which Kt═N, P, As, Sb, S or Se, A═N, P, P(O), O, S, S(O), SO₂, As, As(O), Sb or Sb(O), R¹, R², R³ and R⁴ are identical or different and are H, halogen, substituted and/or unsubstituted alkyl C_(n)H_(2n+1), substituted and/or unsubstituted C₁₋₁₈-alkenyl having one or more double bonds, substituted and/or unsubstituted C₁₋₁₈-alkynyl having one or more triple bonds, substituted and/or unsubstituted cycloalkyl C_(m)H_(2m−1), monosubstituted, polysubstituted and/or unsubstituted phenyl, substituted and/or unsubstituted heteroaryl; where n=1-18, m=3-7, x=0 or 1, y=1-4,y=1 for x=0, where b, c, d and e are each =0 or 1, where b+c+d+e≠0, A may be included in various positions in R¹, R², R³ and/or R⁴, Kt may be included in a cyclic or heterocyclic ring, the groups bonded to Kt may be identical or different.
 5. Process according to one of claims 1 to 4, characterised in that the conversion to a bis(trifluoromethyl)imido salt of the general formula (I) is carried out at a temperature of from −60 to +60° C., preferably from −50 to +50° C., particularly preferably at from −45 to +30° C.
 6. Process according to one of claims 1 to 5, characterised in that the conversion to a bis(trifluoromethyl)imido salt of the general formula (I) is carried out in an organic solvent, preferably in a polar organic solvent.
 7. Process according to claim 6, characterised in that the solvent used is acetonitrile, benzonitrile, dimethoxyethane and/or propionitrile or a mixture of acetonitrile, benzonitrile, dimethoxyethane and/or propionitrile.
 8. Process according to one of claims 1 to 7, characterised in that the solvent comprises ≦0.1% by weight, preferably ≦0.01% by weight, particularly preferably ≦0.005% by weight, of water.
 9. Process according to one of claims 1 to 8, characterised in that the trifluoromethanesulfonate salt of the general formula (II) or the bis(trifluoromethyl)imidorubidium is employed in a molar excess of ≦3% or in equimolar amounts.
 10. Process according to one of claims 1 to 9, characterised in that the bis(trifluoromethyl)imido salt of the general formula (I) is purified by filtration, preferably by filtration at a temperature of from −90 to +30° C., particularly preferably at from −70 to +20° C., after removal of the solvent.
 11. Process according to one of claims 1 to 10, characterised in that the bis(trifluoromethyl)imido salt of the general formula (I) is purified by extraction with dichloromethane and/or hexane and/or diethyl ether.
 12. Compounds of the general formula (I) M^(a+)[(N(CF₃)₂)⁻]_(a)  (I) in which M═Cd²⁺, Zn²⁺or Cu⁺.
 13. Electrolyte comprising at least one salt of the general formula (I) prepared according to claim
 1. 14. Use of the electrolyte according to claim 13 in electrochemical cells.
 15. Electrochemical cells, in particular capacitors and supercapacitors, containing an electrolyte according to claim
 13. 